The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Vehicles include an internal combustion engine that generates drive torque. An intake valve is selectively opened to draw air into cylinders of the engine. The air is mixed with fuel to form a combustion mixture. The combustion mixture is compressed within the cylinders and is combusted to drive pistons within the cylinders. An exhaust valve is selectively opened to allow exhaust gas to exit the cylinders after combustion.
A rotating cam shaft regulates the opening and closing of the intake and exhaust valves. The camshaft includes a plurality of cam lobes that rotate with the camshaft. The profile of the cam lobe determines a valve lift schedule. The valve lift schedule includes the amount of time that the valve is open (duration) and the magnitude or degree at which the valve opens (lift).
Variable valve actuation (WA) technology improves fuel economy, engine efficiency, and/or performance by modifying a valve lift event, timing, and duration as a function of engine operating conditions. Two-step WA systems include variable valve lift mechanisms such as hydraulically controlled switchable roller finger followers (SRFFs). SRFFs enable two discrete valve states (e.g., a low lift state and a high lift state) for the intake and/or exhaust valves.